Magnetic recording/reproducing equipment for computers or the like generally drives a magnetic disk of the hard type having a magnetic layer on a rigid substrate relative to a flying magnetic head for magnetic recording/reproducing purposes.
Most magnetic disks used in the past were of the coating type. To meet a demand for increasing the capacity of magnetic disks, magnetic disks of the thin film type now find increasing use. The thin film type magnetic disks have a magnetic thin film, also known as a continuous thin film, which is formed by vapor phase deposition techniques such as sputtering. They have excellent magnetic properties and increased recording density.
The thin film type magnetic disks most often use modified substrates including aluminum alloy substrates having an Ni-P undercoat layer plated thereon or a hard oxide layer formed by anodization. A Cr under layer, a metallic magnetic layer such as a Co-Ni layer and a protective lubricant layer of carbon or the like are consecutively deposited on the substrate as by sputtering. However, a reliability problem arises because the metallic magnetic layer such as Co-Ni is liable to corrosion and less hard. On the contrary, Japanese Patent Application Kokai Nos. 43819/1987 and 175219/1988 disclose a magnetic thin film based on iron oxide which is chemically stable, resistant against corrosion, and hard enough.
The flying magnetic head has a slider which generates flying forces in an air bearing fashion. The flying magnetic head is generally classified into the composite type in which a core is integrated with the slider and the monolithic type in which a core also serves as the slider.
For maximum density recording, flying thin film magnetic heads have been used in practice. The flying thin film magnetic heads have magnetic pole, gap, coil and other necessary layers formed on a nonmagnetic base by vapor phase deposition, wet plating and other techniques. In these flying thin film heads, the base plays the role of a slider.
A magnetic disk equipment drives a magnetic disk relative to a flying magnetic head in a contact start and stop (CSS) manner so that an impact is applied to the magnetic layer of the disk upon starting and stopping because the floating surface of the magnetic head (or the surface of the slider facing the magnetic disk) rests on the magnetic disk before and after the operation. This tendency is aggravated particularly when a flying thin film magnetic head is used. The magnetic layer undergoes more impact upon CSS because the spacing or flying height between the magnetic disk and the magnetic head is minimized for high density recording.
The minimized flying height leaves a risk of accidental contact between the magnetic disk and the flying magnetic head during operation due to vibration of the magnetic disk or any externally applied impact.
A magnetic disk having an iron oxide base magnetic thin film as disclosed in Japanese Patent Application Kokai Nos. 43819/1987 and 175219/1988 uses a glass substrate having a mirror finished surface so that the magnetic layer has a surface roughness (Rmax) as low as up to 100 .ANG.. The magnetic disk of this type allows the flying height to be set minimal although the magnetic layer would be more severely damaged if undesired accidental contact occurred between the disk and the head upon CSS or during operation.
Japanese Patent.Application Kokai Nos. 43819/1987 and 175219/1988, however, do not refer to the durability of the magnetic layer. No effective proposal for increasing the durability of an iron oxide base magnetic layer of the continuous thin film type is available as far as the inventors know.
The inventors have proposed a magnetic recording medium in which the surface roughness (Rmax) of a glass substrate on its surface is limited to a specific range as well as the surface roughness (Rmax) of the medium in U.S. Ser. No. 354,375 filed May 19, 1989 and a magnetic recording medium in which the area proportion of specific peaks of .gamma.-Fe.sub.2 O.sub.3 in the magnetic layer is limited and .alpha.-Fe.sub.2 O.sub.3 is additionally introduced in the magnetic layer in copending U.S. application filed Ser. No. 514,401 filed Apr. 26, 1990.
Since the general demand for high density recording is toward minimization of the flying height, there is a need for a magnetic recording medium having higher CSS durability. A minimized loss of electromagnetic properties at higher frequencies, that is, a flatter frequency response is desired for high density recording.